Finally the lamp lit up at 610km.

Thats an increase of at least 60km per tank.
Or in other words:
Before the mod it was 11 litres / 100km - Now its 10 litres / 100km.

Thanks to all the guys that encouraged me with their explainations and how-to-do-guides to do this mod!

Now I can save money to get me those awsome altezza tail lights soon... ;)

Uli